Electrical safety methods, devices, and systems for medical treatment devices

ABSTRACT

Systems, methods, and devices can detect a dangerous or adverse condition or anticipated condition that indicates an undesirable amount of electric current in a patient-connected tube providing fluid to a patient. The fluid flow to the patient is stopped responsive to the detection. Stoppage of fluid flow to the patient can reduce or prevent electric current in the fluid from reaching a patient, flowing through the patient to ground, and/or continuing to flow through the patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage entry of InternationalApplication No. PCT/US12/41740 filed Jun. 8, 2012, which claims thebenefit of U.S. Provisional Patent Application No. 61/494,770 filed Jun.8, 2011 and U.S. Provisional Patent Application No. 61/590,409 filedJan. 25, 2012, all of which are incorporated herein by reference intheir entireties.

FIELD

The disclosed subject matter involves electrical safety methods,devices, and systems for medical treatment devices, and moreparticularly deals with systems, methods, and apparatuses that preventand/or stop electric current from flowing from medical electrical (“ME”)equipment to a patient connected to the medical electrical equipment.

BACKGROUND

The use of electrically powered medical devices or equipment (ME)connected to a patient is very common in modern medicine. Along with thebenefits these devices are designed to bring to a patient, they also cancreate a potential hazard of electric shock to the patient. Electricshock can be caused by leakage current flowing through the patient'sheart, for instance, creating ventricular defibrillation, which amedical device may induce in an earthed patient or sink to earth if thepatient is in contact with another source of electricity. Electricalmedical equipment standards are developed to minimize this hazard byspecifying safe levels of patient leakage current flowing throughpatient applied parts of medical devices in no fault and specific faultconditions.

Accordingly, prevention and protection against electrical shock orleakage currents is a significant consideration in the design of medicalelectrical equipment. Leakage currents for medical electrical equipmentmay be defined by the path current takes and can include earth leakagecurrent, enclosure leakage current (or touch current), patient leakagecurrent, patient auxiliary leakage current, and mains voltage to appliedpart leakage current.

Most medical electrical equipment or devices have contact with a deviceoperator, a patient, or both. Though leakage currents typically aresmall, the amount of current required to produce adverse physiologicaleffects on a human body is also small, so such leakage currents must belimited to safe values by the design of medical electrical equipment.Accordingly, medical electrical devices must be designed to pass certaintests to ensure that excessive leakage current does not dissipate fromthe mains, the device enclosure, or applied parts to and through a humanbody. Portions of Standard ANSI/AAMI/IEC 60601, for instance, addresssafety requirements for medical electrical equipment.

Medical electrical equipment has a designated class and type, withcategorization into class being based on the form of protection usedagainst electrical shock or leakage current and type designation beingdefined by the degree of protection from electrical shock or leakagecurrent.

Class I medical electrical equipment has a protective earth connection.The primary means of protection for Class I medical electrical equipmentis the insulation between “live” parts and exposed conductive parts,such as a metallic enclosure. Supplemental protection is provided by theprotective earth connection. Fault or leakage current can flow from themains to earth via the protective earth conductive connection, whichcauses a protective device (e.g., a circuit breaker or a fuse) todisconnect the medical electrical equipment from the supply. Note, ofcourse, that not all medical electrical equipment having a protectiveearth connection necessarily is classified as Class I medical electricalequipment.

Class II medical electrical equipment, on the other hand, does not havea protective earth, and protection against electrical shock is providedby reinforced insulation or double insulation. For double insulation,primary protection is provided by a first layer of insulation (includingair) and secondary protection is provided by a second insulation layer.Leakage current can flow from Class II medical electrical equipment.

Different types of medical electrical equipment include B, BF, and CF,with each type affording a different degree of protection againstelectrical shock or leakage current. Generally speaking, B is formedical electrical equipment providing a particular degree of protectionagainst electrical shock, particularly regarding allowable leakagecurrents and reliability of the protective earth connection (ifpresent). BF is as type B, but with isolated or floating (F-type)applied part or parts. CF provides a higher degree of protection againstelectrical shock than BF, particularly with regard to allowable leakagecurrents and has floating applied parts. Incidentally, an applied partmay be defined as a part of the medical electrical equipment which innormal use necessarily comes into physical contact with the patient forthe equipment to perform its function or can be brought into contactwith the patient or needs to be touched by the patient.

SUMMARY

The Summary describes and identifies features of some embodiments. It ispresented as a convenient summary of some embodiments, but not all.Further the Summary does not necessarily identify critical or essentialfeatures of the embodiments, inventions, or claims.

Generally speaking, embodiments of the disclosed subject matter includesystems, methods, and devices that can detect a medical electricalapparatus fault or an external fault that can potentially cause or hascaused an increase in patient leakage current flowing in anon-conductive tube or tubes respectively filled with conductive liquidconnecting a patient to the medical electrical apparatus, and responsiveto the detection, mechanically break the continuity of the fluid in thetube or tubes. Such breaking of continuity can interrupt or prevent thepassage of patient leakage current and thus stop or prevent electricshock to the patient.

Included among embodiments described herein are a method for protectinga patient from an electrical source, comprising: connecting the patientto a treatment device by a fluid line; receiving a voltage or currentsignal indicating a flow of current or voltage in the fluid lineconnected to the patient; determining if the voltage or current exceedsa predetermined threshold; and in response to the determining, closing avalve to break continuity between the patient and the treatment device.In various embodiments, a human perceptible output indicating thedetected voltage or current may be generated.

Also, in embodiments, a system for protecting a patient from anelectrical source, comprising: means for receiving a voltage or currentsignal indicating a flow of current or voltage in a fluid line connectedto the patient; means for determining if the voltage or current exceedsa predetermined threshold; and means for closing a valve to breakcontinuity between the patient and the treatment device in response tothe determined voltage or current. Optionally, the system may furthercomprise means for generating a human perceptible output indicating thedetected voltage or current.

Embodiments also include a system for stopping flow of a conductivefluid to a patient, comprising: means for identifying an unsatisfactorycondition in the system indicative of patient leakage current oranticipated patient leakage current of an unacceptable amount; means forstopping fluid continuity to the patient based on the identifiedunsatisfactory condition. Optionally, the means for stopping the fluidflow continuity to the patient mechanically interrupts the fluidconductive path to the patient. Further, the means for stopping thefluid flow continuity to the patient can include one or more of apinching apparatus that pinches closed a corresponding fluid flow line,a valve to break continuity between patient and a treatment device, afolding apparatus to fold the tube to close the corresponding fluid flowline, and a bubble introducing apparatus to introduce air into the fluidflow line to form an air break. Optionally or alternatively, the meansfor stopping the fluid flow continuity to the patient includes a valveto divert flow to a circuit having an air break. The circuit may have adrip chamber. The system can also comprise means for handling fluidcoupled to the patient via one or more patient fluid flow lines, whereinnormal operation of the fluid handling means can be interruptedresponsively to the unsatisfactory condition indication. Optionally, themeans for stopping fluid continuity to the patient may include redundantdevices of same or different types for stopping fluid continuity.Further, stopping fluid continuity to the patient can prevent or stopelectric shock to the patient.

In one or more embodiments, the unsatisfactory condition can be one ormore of a sensed patient leakage current exceeding a predeterminedamount, a sensed voltage differential associated with the patientleakage current exceeding a predetermined amount, a fault condition, ananticipated fault condition, a sensed change in fluid conductivity, aloss of earth, and vibration. Optionally, the unsatisfactory conditionindication may be predictive of a harmful, dangerous, or adversesituation to the patient.

Optionally, the fluid continuity may be temporarily interrupted withoutshutting down means for supplying conductive fluid to the patient,wherein, once the unsatisfactory condition is resolved, the fluidcontinuity to the patient can be restored. Further, the system may beoperative to stop fluid continuity to the patient when a fluid treatmentmachine thereof sinks to earth patient leakage current caused byexternal voltage applied to the patient.

In one or more embodiments, the acceptable amount of patient leakagecurrent is zero. Alternatively, the acceptable amount of patient leakagecurrent is 10 μA or below or below 10 μA. Optionally, the means forstopping fluid continuity to the patient causes reduction of patientleakage current to keep within or reduce to an acceptable limit.

In one or more embodiments, optionally, the means for identifying anunsatisfactory condition in the system includes one or more of at leastone sensor disposed external to means for handling fluid and operativeto sense a characteristic of a fluid line providing the conductive fluidto the patient; at least one sensor disposed internal to the means forhandling fluid and operative to sense a characteristic of said means forhandling fluid indicative of patient leakage current or an anticipatedoccurrence of patient leakage current; and at least one sensor disposedon or in association with the patient to sense indications of patientleakage current or an anticipated occurrence of patient leakage current.

Embodiments also can include a method for preventing or minimizingpatient leakage current, comprising: identifying an indication ofpatient leakage current or a precursor to an unacceptable leakagecurrent situation; and making discontinuous a fluid path to a patientresponsive to said identifying.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will hereinafter be described in detail below with referenceto the accompanying drawings, wherein like reference numerals representlike elements. The accompanying drawings have not necessarily been drawnto scale. Any values dimensions illustrated in the accompanying graphsand figures are for illustration purposes only and may not representactual or preferred values or dimensions. Where applicable, somefeatures may not be illustrated to assist in the description ofunderlying features.

FIG. 1A is a schematic representation of patient leakage current in amedical system where an internal electrical or power source causes thepatient leakage current.

FIG. 1B is a schematic representation of patient leakage current in amedical system where an external electrical or power source causes thepatient leakage current.

FIG. 2A is a diagrammatic representation of the schematic representationof FIG. 1A.

FIG. 2B is a diagrammatic representation of the schematic representationof FIG. 1B.

FIG. 3 is a block diagram of a system according to embodiments of thedisclosed subject matter.

FIG. 4 shows diagrammatic and schematic portions of a system accordingto one or more embodiments of the disclosed subject matter.

FIG. 5 shows diagrammatic and schematic portions of a system accordingto one or more embodiments of the disclosed subject matter.

FIG. 6A shows a portion of a sensor according embodiments of thedisclosed subject matter.

FIG. 6B shows another portion of a sensor according to embodiments ofthe disclosed subject matter.

FIG. 7 is a flow chart of a method according to embodiments of thedisclosed subject matter.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thedisclosed subject matter and is not intended to represent the onlyembodiments in which the disclosed subject matter may be practiced. Thedetailed description includes specific details for the purpose ofproviding a thorough understanding of the disclosed subject matter.However, it will be apparent to those skilled in the art that thedisclosed subject matter may be practiced without these specificdetails. In some instances, well-known structures and components areshown in block diagram form in order to avoid obscuring the concepts ofthe disclosed subject matter.

Generally, an aim of one or more embodiments of the disclosed subjectmatter is to prevent and/or stop unwanted electric current flow (e.g.,any current or current above a specified threshold) through a patientvia conductive fluid connections between the patient and the medicalelectrical fluid handling equipment.

Medical electrical equipment or systems may be connected to a patient byone or more non-conductive tubes filled with conductive fluid. Someexamples of such equipment or systems include infusion pumps,intravenous pumps, dialysis machines, medical fluid warmers,extracorporeal blood treatment, surgical red blood cell saving,intro-operative and post-operative vacuum suction, and donor apheresismachines. The non-conductive tubes connecting these machines to apatient under treatment may become conductors of electricity, especiallyin the case where the fluids in the tubes have a significantconcentration of dissolved ionic species. In some instances, these tubesmay be the only electrically conductive connection between the patientand the medical electrical equipment, for example, where the connectionto the patient applied part, such as intravenous needle or catheter, isrepresented by non-conductive tubes filled with conductive fluidcreating a path for the patient leakage current. The tubes can couplevoltage induced to the fluid from the medical electrical equipment tothe patient. If the patient is connected to a grounded hospital bed orany other conductive apparatus, for instance, thereby closing thecircuit, potentially harmful electric current can flow through thepatient.

Another potentially dangerous situation can exist when a patientconnected to a fluid handling medical device with tubes that are filledwith conductive liquid is subject to the influence of an externalvoltage source, such as a malfunctioning electrical utility device. Insuch a case, the fluid handling medical device may close the electriccircuit by coupling the conductive fluid flowing through the device tothe AC Mains ground feeding it. The current flowing through the patientin the above described situations is known as patient leakage current,with allowable patient leakage current values being specified bynational and international standards for medical electrical equipment(as discussed above).

Medical fluid handling apparatus functional requirements can dictate thedesign configurations which may create electrical coupling between adevice's electric circuitry and physiological and treatment fluids. Insome instances a medical fluid handling apparatus may be required toprovide the fluidic path sterility. To achieve this frequently thefluidic path comprises a sterile disposable, constructed from hardplastic parts and tubing, for instance. These materials are usually goodelectrical isolators so energy transfer between fluid flowing in themachine and the machine circuitry is frequently only a result ofcapacitive or inductive coupling.

Embodiments of the disclosed subject matter include systems, methods,and devices that can detect medical electrical apparatus fault(s) and/orexternal fault(s) that potentially can cause or has/have caused patientleakage current or an unacceptable increase in or amount of patientleakage current flowing in a non-conductive tube or tubes respectivelyfilled with conductive liquid connecting a patient to the medicalelectrical apparatus. Responsive to the detection, fluid flow to thepatient can be temporarily interrupted, thereby preventing or stoppingpatient leakage current and preventing or stopping electric shock to thepatient.

In one or more embodiments of the disclosed subject matter, normaloperation of fluid handling equipment is interrupted upon sensing ordetection of patient leakage current. Optionally or alternatively,normal operation of fluid handling equipment is interrupted upondetection of a potentially adverse or dangerous condition that mostlikely has led, may lead, or will lead to creation of patient leakagecurrent. Once the adverse or dangerous condition is resolved, normaloperation of the fluid handling equipment may resume. Interruption ofnormal operation can mean stopping fluid flow to a patient, but notnecessarily shutting down or shutting down completely the fluid handlingequipment. Stopping fluid flow to the patient can include one or more ofbreaking continuity in the fluid line and diverting fluid away from thepatient as discussed herein. Examples of adverse or dangerous orpotentially adverse or dangerous conditions can include an overcurrent,an undercurrent, a change in liquid conductivity, loss of earth, motorvibration, etc.

In one or more embodiments of the disclosed subject matter, an electriccurrent flow in a non-conductive tube filled with conductive liquid canbe sensed, detected, or otherwise identified, and said current can bereduced or interrupted by mechanically breaking the continuity of thefluid in the tube. For example, this can be accomplished in one or moreembodiments, by closing a valve, pinching off the tube, or folding thetube. Additional non-limiting examples are set forth herein. In medicalapplications it may be preferable to use a pinch valve for this purposeto avoid introduction of wetted components into the flow passage, forexample. Such mechanical breaking of continuity can electrically isolatethe inlet and outlet fluid volumes.

Breaking continuity of a fluid flow tube (or line) to prevent electriccurrent flowing through to the patient can be advantageous because thefluidic lines may be the only electrical conductors connecting a medicalfluid handling electrical device to a patient under treatment. As setforth herein, other ways may be employed to handle patient leakagecurrent. For example, optionally or alternatively, the fluid flow can bererouted from the patient.

Breaking continuity of a conductive flow or rerouting the conductiveflow from the patient may be a preferred way to prevent patientelectrical shock as opposed to shutting down the machine partially orentirely. Reasons can include: (1) shutting down the machine orapparatus may not remove the hazard of electric shock to the patient. Anexample of this is when a medical machine or apparatus sinks to earthpatient leakage current caused by external voltage applied to thepatient; (2) it may be beneficial not to shut down completely themedical machine or apparatus so patient treatment can be quickly resumedwithout restarting the machine once the fault condition is removed.

As indicated above, breakage of the conductive fluid path can betriggered by one or more of a measured voltage, current, and fluidconductivity in the tube, for instance. One or more of such measurementscan be taken proximate the tube. Thus, embodiments of the disclosedsubject matter also can include one or more voltage detection sensorsand/or one or more current detection sensors to provide protectionagainst the electrical hazard described above. That is, thecorresponding sensor(s) can be arranged proximate the tube. Note alsothat the trigger does not necessarily need to be voltage, current, orfluid conductivity. Further, one or more sensors as set forth herein canbe elsewhere on a medical machine and/or on the patient. Modifyingcircuits can be electrically coupled to the sensor(s) and may controlthe mechanical “closing” apparatus (e.g., a valve, a pinch, etc.), suchthat it closes, once a possibility of potentially dangerous patientleakage current increase is detected or in-fact occurs.

Further, embodiments of the disclosed subject matter can also implementmeans to reduce patient leakage current to acceptable limits, such asisolated electrical AC/DC and/or DC/DC power supplies to reduce theelectrical voltage induced to the isolated section of the supplies.Isolated power supplies can be employed to prevent unwanted patientleakage currents (e.g., any current or current above a specifiedthreshold). Detection and shutoff circuitry and methods can also protectagainst leakage current when external voltage is applied to the patient.

Additionally, one or more embodiments of the disclosed subject mattercan reduce patient leakage current to an acceptable limit. Suchreduction can be implemented using one or more air gap fluid handlingdevices or apparatuses, for example, included in the medical electricalapparatus fluidic path. Air gap fluid handling devices can be employedto prevent unwanted patient leakage currents (e.g., any current orcurrents above a specified threshold) flowing from the parts of thesystem (or a portion thereof, such as a device, machine, or apparatus)that require the application of electrical signal to the fluid and/orhave a strong parasitic coupling to any electrical signals within themedical apparatus due to its design dictated by functional requirements,for instance. Detection and shutoff circuitry and methods thereof can beused to provide protection redundancy and/or to supplement protectionprovided by air gap devices.

According to embodiments of the disclosed subject matter, normaloperation of fluid handling medical equipment is interruptedresponsively to over current or an over voltage condition or anindication that such a condition is imminent or likely at a future timeand resumed once the condition or risk of the condition arising ends orfalls below an acceptable threshold level.

According to further embodiments of the disclosed subject matter, anelectric current flow in a non-conductive tube filled with conductiveliquid may be reduced or interrupted by mechanically breaking thecontinuity of the fluid in the tube. For example, this can beaccomplished in embodiments, by closing a valve, pinching off the tube,folding the tube, introducing air into the tube to form an air break,diverting flow to a circuit having an air break (such as a dripchamber), or other ameliorative device.

In practical applications for medical applications it may be preferableto use a pinch valve for this purpose for a variety of reasons,including, convenient control, cost, and because it avoids the need foradditional wetted components in the flow passage. Such mechanicalbreaking of continuity is effective for electrically isolating the endsof a fluid circuit broken by such a pinch clamp.

FIG. 1A shows a schematic representation associated with a patientleakage current path when the patient is earthed, through a hospitalbed, for instance, and voltage is induced in the fluid via parasiticelectric coupling between the fluid flowing inside the medical apparatusand current carrying parts of this apparatus. FIG. 1B shows a schematicrepresentation associated with a patient leakage current path when thepatient is touching an external source of electricity and the medicaldevice sinks current to earth.

According to IEC 60601 Standard, for instance, the patient leakagecurrent through patient applied part(s) located close to a patient'sheart should not exceed 10 μA in no-fault and 50 μA in a faultcondition. In one or more embodiments of the disclosed subject matter,it is desirable to detect these levels of current flowing throughconductive fluid inside a non-conductive tube. Coupling impedanceZcoupling between the conductive fluid and the medical apparatus isusually high. This impedance can be treated as a shunt resistor todetect patient leakage current by measuring the voltage drop acrossZcoupling, ΔVcoupling, as shown on FIGS. 1A and 1B, created by thiscurrent. The current measurement may be replaced by a differentialvoltage measurement. The voltage levels are usually relatively high dueto the Zcoupling high values. As can be seen from FIGS. 1A and 1B thesame differential voltage measurement will work for both cases.

Referring to FIG. 1A, the patient leakage current path 309 includesearth (i.e., ground) 302; a power or electrical supply 303 of a medicalmachine or apparatus (i.e., an internal power supply); the medicalmachine or apparatus, which is represented by its impedance 304 (Zsource); a coupling impedance 305 (Z coupling) associated with an outputof the power supply 303, typically the capacitive coupling between thefluid flowing inside of the medical machine or apparatus and parts ofthe medical machine or apparatus conducting or cable of conductingelectricity; the patient, which is represented by impedance 306 (Zpatient); and then to ground 307. Ground 307 can represent the patient's“earthed” condition, for instance through a hospital bed as indicatedabove. Voltage is induced in the fluid via parasitic electric couplingbetween the fluid flowing inside the medical apparatus line and currentcarrying parts of this machine. Ground 302 and 307 can be the same earthground. A voltage difference 308 for the coupling impedance 305 isindicated (ΔVcoupling).

Referring to FIG. 1B, the patient leakage current path 309 includesearth (i.e., ground) 302; an external power or electrical supply 310;the medical machine or apparatus, which is represented by its impedance304 (Z source); the patient, which is represented by impedance 306 (Zpatient); a coupling impedance 305 (Z coupling); and ground 307, whichcan represent an external power supply. External power supply 310 may befrom a broken utility device, for instance. In FIG. 1B, a power sourceinside the medical machine or apparatus in not inducing patient leakagecurrent. A voltage difference 308 for the coupling impedance 305 isindicated (ΔVcoupling).

FIGS. 2A and 2B show different diagrammatic representations of systems,methods, and devices for sensing or detecting patient leakage current topatient 200 fluidly connected to treatment machine 102 via fluid path101 under differing circumstances. FIG. 2A is represented schematicallyby FIG. 1A, and FIG. 2B is represented schematically by FIG. 1B.Circumstances caused by a voltage from machine 102 being coupled to thefluid line 101 (e.g., FIG. 2A), and circumstances caused by a voltage300 external to machine 102 coupled to fluid line 101 (e.g., FIG. 2B).FIGS. 2A and 2BC include a voltage sensor 110, though as discussedherein embodiments are not limited to voltage sensors.

FIG. 3 is a block diagram of a system 100 according to embodiments ofthe disclosed subject matter.

The system 100 includes a treatment device 102, a controller 104 (e.g.,a microprocessor, ASIC, FPGA, etc.), an electro-mechanical means 106(e.g., a valve, a pinch, a fluid rerouting apparatus), anon-electrically conductive fluid conductor 101 (e.g., plastic tubing),and a sensing element 110 (e.g., a non-invasive capacitive voltage orcurrent sensor). The fluid conductor 101 may be physically coupled to apatient 200 via a cannula, for example (not explicitly shown).

The sensor 110 can measure or detect signals associated with the flow ofconductive fluid or liquid through fluid conductor 101. Examples ofconductive fluid include blood or treatment. For example, sensor 110 cansense or detect a corresponding voltage, a corresponding current, and/ora corresponding change in fluid conductivity of the fluid flowingthrough the fluid conductor 101.

In various embodiments, multiple sensors 110 of same or differingconfigurations may be employed along the fluid conductor 101 atdifferent positions. Multiple sensors 110 may be employed as part of afailsafe system should one or more of the sensors malfunction.Additionally, multiple sensors 110 may be employed to ensure localizeddetection. Optionally or alternatively, additional sensors or sensorcircuitry 111 can be implemented, which can detect fault conditions orpotential fault conditions associated with treatment device 102.Optionally or alternatively, additional sensors or sensor circuitry 112can be implemented on or with patient 200 to detect fault conditions orpotential fault conditions. Optionally or alternatively, adverse ordangerous, or potentially adverse or dangerous conditions may be sensed,detected, or otherwise identified by sensors 110, 111, and 112.

The measured signals may be fed to the controller 104 or a simplecircuit. The controller 104 may execute an algorithm or the simplecircuit can detect a threshold signal level, which may indicate thedetected electrical signal is at or above a predetermined threshold. Invarious embodiments, the predetermined threshold can be based on aminimum level of current capable of causing physiological damage to thepatient and/or in accordance with a governmental standard patientleakage current value.

In various embodiments, the system may be equipped with anelectro-mechanical means 106, such as a valve or a fluid isolationactuator, to interrupt the conductive fluid path as commanded by outputsignal(s) from controller 104. The output signal(s) from the controller104 can be based on the sensed or detected electrical signal from theone or more sensors 110, 111, and/or 112. Once the controller 104identifies a triggering condition, it can command the electro-mechanicaldevice 106 to interrupt the fluidic path to prevent an unacceptable orundesirable electric current flow to and/or through the patient 200. Invarious embodiments, multiple electro-mechanical devices 106 of same ordiffering configurations may be employed along the fluid conductor 101at different positions. Interruption of the fluid path can includererouting of the fluid such that fluid no longer flows to the patient200.

The 110 sensor can be constructed in such a way that it has a relativelyhigh level of electrical impedance to the patient 200, medical deviceelectric circuit, AC Mains, and electrical ground. Such construction canprevent the sensor 110 from creating additional patient leakage current.If the sensor 110 entails inducing an electric signal (voltage orcurrent) into a patient 200 to perform the measurement, such as patientimpedance to earth measurement, the excitation measurement signal levelsshould not create any or any unacceptable patient leakage current.

In addition, the sensor 110 can be placed relatively closer to thepatient connection on the fluidic line 101 than the electro-mechanicaldevice 106. Such a configuration can allow monitoring of patientcondition, while the fluid line 101 is not connected to the patient 200during the system startup or after a protection circuit goes off.Optionally, placing sensor 110 further away from the patient connectionthan the electro-mechanical device 106 may be required if the sensordesign does not meet certain electrical insulation impedancerequirements. In this case the controller 104 can have a software-,hardware-, or combination software/hardware-implemented resettable latchthat can latch an alarm condition, and that may be reset by means otherthan a signal of the sensor 110 to allow the treatment device 102operation to resume once the dangerous condition has been cleared. Forexample, reset may be accomplished by a manual control to ensure theproblem has been acknowledged by an operator.

FIG. 4 shows an example of sensor 110 from FIG. 3. Specifically, FIG. 4shows a non-invasive capacitive voltage sensor that can be used tomeasure the voltage drop created by the patient leakage current acrossimpedance Zcoupling. Non-conductive tube 1 contains conductive fluid 2flowing to the patient applied part (not shown on the drawing). Voltagesource 3, which can represent voltage created by an external source thatthe patient touches, may be connected (i.e., capacitively coupled) tofluid 2. The patient leakage current path is created by the couplingimpedance Zcoupling 7 between conductive fluid 2 and a conductive part 8of the medical apparatus adjacent to tube 1. Conductive part 8 can beconnected to earth 4 (though not necessarily directly). A capacitivesensor 6 comprising a u-shaped conductive electrode 5 with tube 1inserted in it, for example, has an equivalent capacitance Csensor 6between conductive fluid 2 and electrode 5. Electronic circuit 9 cancondition and amplify the capacitive sensor output signal and generateoutput signal Vout 14, which can be fed to a controller (e.g., 104 inFIG. 3) that compares it to a predetermined threshold value (e.g., asafe threshold value or a threshold value in accordance with a Standard)and makes the decision when to activate the mechanism (e.g.,electro-mechanical device 106 in FIG. 3) to stop fluid flow to thepatient. Electronic circuit 9 may be constructed and operative as aninverting amplifier based on operational amplifier 11 fed by bipolarisolated DC power supply 15. A value of feedback capacitor Cfeedback 12impedance may be much lower in the frequency range of interest than thevalue of bias resistor Rbias 13. Bias resistor 13 can serve the purposeof returning the bias current of operational amplifier 11 invertinginput. Electronic circuit 9 can have an isolated ground plane 10 that isconnected to the conductive part 8 of the medical apparatus. Thefollowing equation can represent the relationship between Vout 14 andpatient leakage current designated as Ileak:V _(out) −I _(leak) *Z _(coupling)*(C _(sensor) /C _(feedback))

Accordingly, electronic circuit 9 can measure patient leakage current,as described by the equation above, in the event when patient leakagecurrent is induced by the voltage source within a medical apparatus andflows into an earthed patient. In this case, the voltage source will beconnected to a conductive part 8 of the medical apparatus (notnecessarily directly) and conductive fluid 2 will be connected to earth4 through the patient impedance.

FIG. 5 shows another possible implementation of an electronic circuit 9for a non-invasive capacitive voltage sensor that can be used to measurethe voltage drop created by the patient leakage current across impedanceZcoupling. Similar to FIG. 4, non-conductive tube 1 can containconductive fluid 2 flowing to the patient applied part (not shown). Acapacitive sensor comprising a u-shaped conductive electrode 5 with tube1 inserted in it can be provided and can have an equivalent capacitanceCsensor 6 between conductive fluid 2 and electrode 5. Voltage source 3,representing voltage created inside the medical electrical fluidhandling device, is shown connected to a conductive part 8 of themedical apparatus. The patient leakage current path is created by thecoupling impedance Zcoupling 7 between conductive fluid 2 and conductivepart 8 of the medical apparatus adjacent to tube 1. Incidentally,patient isolation impedance to earth is not shown. Electronic circuit 9can condition and amplify the capacitive sensor output signal and cangenerate output signals Vout 14 and Vout_inv 23 fed into a controller(e.g., 104 in FIG. 3) that can compare the values to a predeterminedthreshold value (e.g., a safe threshold value or a threshold value inaccordance with a Standard) and makes the decision when to activate theprotection mechanism (e.g., electro-mechanical device 106 in FIG. 3) tostop fluid flow to the patient. Electronic circuit 9 can output bothinverted and non-inverted signals so that a comparator in the controllercan react to either positive or negative half wave of the AC voltagesignal so as to speed up the response time to a potential or realpatient leakage current situation. Electronic circuit 9 can beconstructed and operative as a non-inverting amplifier based onoperational amplifier 11 fed by bipolar isolated DC power supply 15. Thevalue of divider capacitor Cdivider 18 impedance may be much lower inthe frequency range of interest than the value of bias resistor Rbias19. A capacitive divider formed by the equivalent sensor capacitanceCsensor 6 and capacitor Cdivider 18 can bring the circuit input signalwithin the working range of amplifier 11. Bias resistor 19 can serve thepurpose of returning the bias current of operational amplifier 11 tonon-inverting input. Electronic circuit 9 can have an isolated groundplane 10 connected to the conductive part 8 of the medical apparatus.The following equation can represent the relation between Vout 14 andpatient leakage current designated as I_(leak):V _(out) =I _(leak) *Z _(coupling)*(1+R2/R1)*(C _(sensor)/(C _(sensor)+C _(divider)))

Inverting amplifier 22 can be formed by operational amplifier 22 andresistors 20 and 21. Resistors 20 and 21 may be equal.

Sensor performance can be verified by the medical device during apower-on self-test, for example, before the medical device is connectedto a patient, by providing another u-shaped electrode coupled to thetube and applying the AC voltage to it sufficient to trip the protectioncircuit. The sensing circuit should detect this voltage and activate theprotection mechanism (e.g., electro-mechanical device 106 in FIG. 3).

In the case of voltage detection corresponding to patient leakagecurrent, detected voltage may approach and possibly reach or exceed thelevel calculated by the following formula:V _(trip) =I _(leak limit) *Z _(coupling),

where V_(trip)=controller High Limit Alarm Voltage triggering shutoffreferenced to Earth; I_(leak limit)=Patient Leakage Current Limit,defined by a medical equipment safety standard, for example; andZ_(coupling)=coupling impedance between fluid flowing to the patientapplied parts and medical fluid handling apparatus electricallyconductive components.

When the detected voltage has reached, is within a certain value fromthe predetermined voltage level V_(trip), or exceeds the predeterminedvoltage level V_(trip), a (e.g., controller 104) can provide controlsignal(s) to cause electro-mechanical device(s) as set forth herein todisconnect the patient fluidic connection, thus preventing any current,an undesirable amount of current, or an excessive amount of current fromreaching and passing through the patient. The treatment device can bethereafter or simultaneously put in a standby mode or turned off, forinstance, until it is determined that a safe condition exits (i.e., noor a suitable amount of leakage current). Thus, the system can protectthe patient from being subjected to any current, an undesirable amountof current, or an excessive amount of current created by voltages bothinternal to the system and applied to the patient externally.

Optionally, embodiments can include at least two measurement devices: afirst measurement device measuring the impedance between patient andEarth, and a second measurement device measuring electric voltageapplied to the patient with respect to earth. The controller 104 cancalculate patient leakage current using the following formula:I _(patient leak) =V _(patient) /Z _(coupling),

where I_(patient leak)=Patient leakage current, as calculated by thecontroller, for example; V_(patient)=Patient voltage measured withrespect to Earth; and Z_(coupling)=coupling impedance between fluidflowing to the patient applied parts and medical fluid handlingapparatus electrically conductive components.

When calculated leakage current approaches, reaches, or exceeds a limitdefined by the standard, for example, a controller can commandelectro-mechanical device(s) as set forth herein to interrupt the fluidconnection to the patient. The treatment device can be thereafter orsimultaneously put in a standby mode or turned off, for instance, untilit is determined that a safe condition exits (i.e., no or a suitableamount of leakage current).

In one or more embodiments, multiple electric conduction paths may existin a fluid handling medical apparatus or device connected to a patient.For some such configurations a reliable way to estimate patient leakagecurrent is to measure electric current flowing in the fluidic linesconnecting machine or device to the patient. If there are multiplefluidic paths and other connections to the patient the sum of currentsmeasured should be less than the dangerous patient leakage currentvalue. A controller can collect and add the current values measured,compare the sum to the limit, and generate shutoff signals to theelectro-mechanical means (e.g., one or more valves associated with eachfluidic line) when the sum of currents is over the limit. Optionally,current signals' phases should be accounted for in such calculation. Areliable electric ground may not be available at the installation site.Thus, embodiments according to the disclosed subject matter can providea patient leakage protection scheme that does not require electricalground reference connection. So the device or machine can be fed from anAC source without functional or protective earth.

FIGS. 6A and 6B show portions of a capacitive liquid AC voltage sensoraccording to embodiments of the present invention.

FIG. 6A shows an example of a metal electrode, which can be mounted in aplastic body of a conductor. Such electrode can form part of acapacitive sensor. FIG. 6B can represent a tube to be filled withconductive fluid, such as water, blood, or treatment. The metalelectrode can be the dimensions shown in FIG. 6A or other suitabledimensions.

Patient leakage current as a result of the external voltage applied tothe patient configuration can be reduced using plastic elements (e.g.,plastic plates) in the construction of the medical equipment to reducethe coupling between the conductive fluid flowing through it andconductive components of the medical equipment and an external powersupply.

FIG. 7 is a flow chart of a method 700 according to embodiments of thedisclosed subject matter. The method can be to protect an inducedelectric current, specification, an induced patent leakage current. Theprovided protection can be before patient leakage current is generated,before it reaches the patient, or after it reaches the patient.

In the method, the patient can be connected to a treatment device via afluid line. Conductive fluid can be sent from a treatment machine to thepatient 702. An adverse or dangerous condition or an anticipated adverseor dangerous condition can be sensed, detected, or otherwise identified704. Patient leakage current above a predetermined threshold is oneexample of an adverse or dangerous condition. Responsive to the sensing,detecting, or identifying, the fluid flow to the patient is stopped 706.Stopping fluid flow to the patient can include breaking the fluidconductive path to the patient and/or rerouting the fluid from thepatient as shown and described herein.

Although particular configurations have been discussed herein, otherconfigurations can also be employed. It is, thus, apparent that there isprovided, in accordance with the present disclosure, medical treatmentdevice electrical safety methods, devices, apparatuses, and systems.Many alternatives, modifications, and variations are enabled by thepresent disclosure. Features of the disclosed embodiments can becombined, rearranged, omitted, etc., within the scope of the inventionto produce additional embodiments. Furthermore, certain features maysometimes be used to advantage without a corresponding use of otherfeatures. Accordingly, Applicant intends to embrace all suchalternatives, modifications, equivalents, and variations that are withinthe spirit and scope of the present invention.

It will be appreciated that portions (including an entire portion) ofany modules, processes, methods, and circuitry described above can beimplemented in hardware, hardware programmed by software, softwareinstructions stored on a non-transitory computer readable medium or acombination of the above.

Having now described embodiments of the disclosed subject matter, itshould be apparent to those skilled in the art that the foregoing ismerely illustrative and not limiting, having been presented by way ofexample only. Numerous modifications and other embodiments (e.g.,combinations, rearrangements, etc.) are within the scope of one ofordinary skill in the art and are contemplated as falling within thescope of the disclosed subject matter and any equivalents thereto. Itcan be appreciated that variations to the disclosed subject matter wouldbe readily apparent to those skilled in the art, and the disclosedsubject matter is intended to include those alternatives. Further, sincenumerous modifications will readily occur to those skilled in the art,it is not desired to limit the disclosed subject matter to the exactconstruction and operation illustrated and described, and accordingly,all suitable modifications and equivalents may be resorted to, fallingwithin the scope of the disclosed subject matter.

What is claimed is:
 1. A method for protecting a patient from anelectrical source, comprising: connecting the patient to a treatmentdevice by a fluid line; receiving a voltage or current signal indicatinga flow of current or voltage in the fluid line connected to the patientfrom a sensor configured to electrically couple to a fluid in the lineto detect current or voltage in the fluid at a position in the fluidline proximate to the sensor; determining if the voltage or currentexceeds a predetermined threshold; and in response to the determining,breaking fluid continuity between the patient and the treatment deviceto halt the flow of current in the fluid carried by the fluid line. 2.The method of claim 1, further comprising generating a human perceptibleoutput indicating the excessive detected voltage or current.
 3. A systemfor protecting a patient from an electrical source, the systemcomprising: a fluid line connected to the patient; a sensor configuredto electrically couple to a fluid in the fluid line and output a voltagesignal or a current signal indicating a flow of current or a voltage inthe fluid at a position in the fluid line proximate to the sensor; meansfor determining if the voltage or the current exceeds a predeterminedthreshold; and means for closing a valve to break continuity between thepatient and the treatment device and halt the flow of current in thefluid carried by the fluid line in response to the determined voltage orcurrent.
 4. The system of claim 3, further comprising means forgenerating a human perceptible output indicating the excessive detectedvoltage or current.
 5. A system for stopping flow of a conductive fluidto a patient, comprising: a sensor configured to be electrically coupledto the conductive fluid in a fluid line identifying an unsatisfactorycondition in the system indicative of patient leakage current oranticipated patient leakage current of an unacceptable amount; and meansfor stopping fluid continuity of the conductive fluid in the fluid linefrom a treatment machine to the patient and halting the flow of currentin the fluid line based on the identified unsatisfactory condition. 6.The system according to claim 5, wherein said means for stopping thefluid flow continuity to the patient mechanically interrupts the fluidconductive path to the patient.
 7. The system according to claim 5,wherein said means for stopping the fluid flow continuity to the patientincludes a pinching apparatus that pinches closed a corresponding fluidflow line.
 8. The system according to claim 5, wherein said means forstopping the fluid flow continuity to the patient includes a valve todivert flow to a circuit having an air break.
 9. The system according toclaim 8, wherein the circuit has a drip chamber.
 10. The systemaccording to claim 5, wherein the unsatisfactory condition is one ormore of a sensed patient leakage current exceeding a predeterminedamount, a sensed voltage differential associated with the patientleakage current exceeding a predetermined amount, a fault condition, ananticipated fault condition, a sensed change in fluid conductivity, adisconnection from ground, and vibration.
 11. The system according toclaim 5, wherein the fluid continuity is temporarily interrupted withoutshutting down a means for supplying conductive fluid to the patient,wherein, once the unsatisfactory condition is resolved, the fluidcontinuity to the patient is restored.
 12. The system according to claim5, wherein the acceptable amount of patient leakage current is zero. 13.The system according to claim 5, wherein the acceptable amount ofpatient leakage current is 10 μA or below 10 μA.
 14. The systemaccording to claim 5, wherein said means for stopping fluid continuityto the patient causes reduction of patient leakage current to keepwithin or reduce to an acceptable limit.
 15. The system according toclaim 5, wherein unsatisfactory condition is a fault condition.
 16. Thesystem according to claim 5, wherein the system is operative to stopfluid continuity to the patient when a fluid treatment machine thereofsinks to earth patient leakage current caused by external voltageapplied to the patient.
 17. The system according to claim 5, furthercomprising means for handling fluid coupled to the patient via one ormore patient fluid flow lines, wherein normal operation of said fluidhandling means is interrupted responsively to the unsatisfactorycondition indication.
 18. The system according to claim 5, wherein theunsatisfactory condition indication is predictive of a harmful,dangerous, or adverse situation to the patient.
 19. The system accordingto claim 5, wherein said means for stopping fluid continuity to thepatient includes redundant devices of same or different types forstopping fluid continuity.
 20. The system according to claim 5, whereinstopping fluid continuity to the patient prevents or stops electricshock to the patient.
 21. The system according to claim 5, wherein saidmeans for identifying an unsatisfactory condition in the system includesone or more of at least one sensor disposed external to means forhandling fluid and operative to sense a characteristic of a fluid lineproviding the conductive fluid to the patient; at least one sensordisposed internal to said means for handling fluid and operative tosense a characteristic of said means for handling fluid indicative ofpatient leakage current or an anticipated occurrence of patient leakagecurrent; and at least one sensor disposed on or in association with thepatient to sense indications of patient leakage current or ananticipated occurrence of patient leakage current.
 22. The systemaccording to claim 5, wherein said means for stopping the fluid flowcontinuity to the patient includes a valve to break continuity betweenthe patient and a treatment device.
 23. The system according to claim 5,wherein said means for stopping the fluid flow continuity to the patientincludes a folding apparatus to fold the tube to close the correspondingfluid flow line.
 24. The system according to claim 5, wherein said meansfor stopping the fluid flow continuity to the patient includes a bubbleintroducing apparatus to introduce air into the fluid flow line to forman air break.
 25. The system according to claim 5, wherein said sensoris a capacitive sensor.